This invention relates to drive train mechanisms for a vehicle, and more particularly, to a drive train mechanism for a vehicle which utilizes pairs of wheels in tandem.
It is well recognized that the tractive efforts of a four or six-wheel vehicle are substantially improved if driving torque is directed to more than one axle of the vehicle. In the case of an articulated vehicle of long wheelbase, wherein the rear wheels are more heavily loaded than the front wheels thereof, steering difficulties are known to exist, such steering difficulties stemming from resistances which are in excess of those normally encountered in shorter wheelbased vehicles. In the case of, for example, a six-wheel vehicle, if all six wheels thereof are rigidly driven, without allowance for differential motion, by the power source of the vehicle, a severe amount of tire scuffing occurs as the vehicle negotiates a turn. Under such conditions, the front wheels of the vehicle must generally run through an arc of greater radius than that of the rear wheels, and therefore would tend to rotate faster than the rear wheels. Also, slight differences in wheel radii caused by inevitable variation in tire inflation, tread wear, or variations in vehicle loads result in what is known as circumferential tire scrub. Under these conditions, a wheel having a smaller radius tends to rotate faster than one having a larger radius while both wheels cover the same distance. If the front and rear wheels are positively driven together without differential action therebetween at the same angular speed, a wheel having a smaller radius will be scraped over the ground surface. It will also be noted that such above-cited problems cause undue stress in the drive system, in turn causing additional friction therein and wear thereof.
Six-wheeled vehicles which provide for differential movement of certain wheels relative to others thereof are disclosed in U.S. Pat. No. 2,667,087 to Myers, U.S. Pat. No. 3,388,760 to Christie and U.S. Pat. No. 3,706,350 to Bokovoy. Each of these patents discloses torque transfer means including differential means associated with pairs of rear vehicle wheels which are disposed in tandem. While the differential action provided between such wheels may be effective in certain uses, it is to be understood that improvements in design for certain applications are continually being sought. In U.S. Pat. No. 2,667,087, it appears that a single differential mechanism connects with axles to drive the front pair and rear pair of rear wheels. It will be understood that such a single differential is not capable of allowing a differential motion across any single rear axle of the pair thereof. In both U.S. Pat. No. 3,388,760 and U.S. Pat. No. 3,706,350, individual differential mechanisms interconnect the forward pair of rear wheels and the rearward pair of rear wheels. However, in either of these patents, a pair of wheels in tandem are interconnected by both above-described differentials, so that an interaction of these two differential mechanisms is involved whenever differential rotation is to be provided between one and the other of a pair of wheels in tandem.
Of more general interest in this area are U.S. Pat. No. 3,457,807 to Altamann, U.S. Pat. No. 3,494,226 to Biddle, U.S. Pat. No. 3,650,349 to Cleveland et al, and U.S. Pat. No. 3,648,545 to Clancey.